refactor(api)!: rename Dictionary => Dict

In the api_info() output:

    :new|put =map(filter(api_info().functions, '!has_key(v:val,''deprecated_since'')'), 'v:val')
    ...

    {'return_type': 'ArrayOf(Integer, 2)', 'name': 'nvim_win_get_position', 'method': v:true, 'parameters': [['Window', 'window']], 'since': 1}

The `ArrayOf(Integer, 2)` return type didn't break clients when we added
it, which is evidence that clients don't use the `return_type` field,
thus renaming Dictionary => Dict in api_info() is not (in practice)
a breaking change.

src/clint.py

@@ -1781,7 +1781,7 @@ def CheckSpacing(filename, clean_lines, linenum, error):
                    r'(?<!\bPMap)'
                    r'(?<!\bSet)'
                    r'(?<!\bArrayOf)'
-                   r'(?<!\bDictionaryOf)'
+                   r'(?<!\bDictOf)'
                    r'(?<!\bDict)'
                    r'\((?:const )?(?:struct )?[a-zA-Z_]\w*(?: *\*(?:const)?)*\)'
                    r' +'